Ultra Low Frequency Sounding and Tomography of Earth Crust

Methods of the ultra low-frequency electromagnetic sounding of the conductivity into the earth crust based on wideband (in the frequency range 0.001-1000 Hz) measurements of electromagnetic fields using both natural and artificial sources of are considered. The inverse problem is solved to retrieve continuous one-dimensional profiles of conductivity using iterative approach for the non-linear integral equation derived from Maxwell´s equations. A tomography method that uses many-frequency data of the 2D electromagnetic scanning along the earth surface is also proposed. The retrieval of the 3D structure of the conductivity in this method is based on the solution of the 3D integral equation that can be reduced to the convolution equation with respect to lateral co-ordinates in the frameworks of Born approximation